Study Design Overview: The goal of this study is to perform a short-term, proof of concept study to examine the safety, tolerability and efficacy of riluzole and D-serine in the treatment of tics. Each medication will be evaluated and compared to placebo as part of a randomized, double-blind, flexible dose, parallel, eight-week protocol, containing six weeks of active treatment (D-serine, riluzole, or placebo). A total of sixty patients (age 8-17 years) with Tourette syndrome or chronic motor tics (Tourette Syndrome Study Group criteria) having moderate to moderately-severe tics will participate; riluzole (n=24), D-serine (n=24), placebo (n=12).